Ruby: missing/lgamma_r.c Source File

Ruby 3.4.7p58 (2025-10-08 revision 7a5688e2a27668e48f8d6ff4af5b2208b98a2f5e)

lgamma_r.c
1/* lgamma_r.c - public domain implementation of function lgamma_r(3m)
2
3lgamma_r() is based on gamma(). modified by Tanaka Akira.
4
5reference - Haruhiko Okumura: C-gengo niyoru saishin algorithm jiten
6 (New Algorithm handbook in C language) (Gijyutsu hyouron
7 sha, Tokyo, 1991) [in Japanese]
8 http://oku.edu.mie-u.ac.jp/~okumura/algo/
9*/
10
11#include "ruby/missing.h"
12/***********************************************************
13 gamma.c -- Gamma function
14***********************************************************/
15#include <math.h>
16#include <errno.h>
17#define PI 3.14159265358979324 /* $\pi$ */
18#define LOG_2PI 1.83787706640934548 /* $\log 2\pi$ */
19#define LOG_PI 1.14472988584940017 /* $\log_e \pi$ */
20#define N 8
21
22#define B0 1 /* Bernoulli numbers */
23#define B1 (-1.0 / 2.0)
24#define B2 ( 1.0 / 6.0)
25#define B4 (-1.0 / 30.0)
26#define B6 ( 1.0 / 42.0)
27#define B8 (-1.0 / 30.0)
28#define B10 ( 5.0 / 66.0)
29#define B12 (-691.0 / 2730.0)
30#define B14 ( 7.0 / 6.0)
31#define B16 (-3617.0 / 510.0)
32
33static double
34loggamma(double x) /* the natural logarithm of the Gamma function. */
35{
36 double v, w;
37
38 if (x == 1.0 || x == 2.0) return 0.0;
39
40 v = 1;
41 while (x < N) { v *= x; x++; }
42 w = 1 / (x * x);
43 return ((((((((B16 / (16 * 15)) * w + (B14 / (14 * 13))) * w
44 + (B12 / (12 * 11))) * w + (B10 / (10 * 9))) * w
45 + (B8 / ( 8 * 7))) * w + (B6 / ( 6 * 5))) * w
46 + (B4 / ( 4 * 3))) * w + (B2 / ( 2 * 1))) / x
47 + 0.5 * LOG_2PI - log(v) - x + (x - 0.5) * log(x);
48}
49
50
51#ifdef __MINGW_ATTRIB_PURE
52/* get rid of bugs in math.h of mingw */
53#define modf(_X, _Y) __extension__ ({\
54 double intpart_modf_bug = intpart_modf_bug;\
55 double result_modf_bug = modf((_X), &intpart_modf_bug);\
56 *(_Y) = intpart_modf_bug;\
57 result_modf_bug;\
58})
59#endif
60
61/* the natural logarithm of the absolute value of the Gamma function */
62double
63lgamma_r(double x, int *signp)
64{
65 if (x <= 0) {
66 double i, f, s;
67 f = modf(-x, &i);
68 if (f == 0.0) { /* pole error */
69 *signp = signbit(x) ? -1 : 1;
70 errno = ERANGE;
71 return HUGE_VAL;
72 }
73 *signp = (fmod(i, 2.0) != 0.0) ? 1 : -1;
74 s = sin(PI * f);
75 if (s < 0) s = -s;
76 return LOG_PI - log(s) - loggamma(1 - x);
77 }
78 *signp = 1;
79 return loggamma(x);
80}
errno
#define errno
Ractor-aware version of errno.
Definition ruby.h:388